Protective flaps on optical plugs have been state of the art and in use for some time. With a few state-of-the-art plugs, the protective flap is connected by means of a linkage to the plug housing. This, for example, is the case with the plug disclosed by EP-A-613 030, wherein the plug can be pivoted about lateral bearing pins that snap into mounting bores. On insertion of the plug into a sleeve portion, guide lugs, likewise arranged laterally, run on a guide member on the sleeve portion and so effect the opening movement of the protective flap. This type of protective flap is not suited to all plug connections, and is particularly unsuited to those connections wherein similar plugs are intended for direct pairing without a separate sleeve portion.
"Research Disclosure" (1987), March, No. 275, New York, discloses a related and comparable plug wherein a screen, formed integrally with the plug casing, is displaced laterally during insertion by means of a corresponding control surface. On withdrawal of the plug, the screen springs back due to the elasticity of its material, and covers the face. A disadvantage of this construction is that the screen or protective flap must be manufactured from the same material as the plug housing; it would, however, be desirable for the plug casing to comprise a very hard material in order to hold the optical fiber holder. A further disadvantage of the state-of-the-art construction is that, as a result of the integral formation of the protective flap, the face of the plug is only covered remotely (screening effect) but, for avoidance of a build up of contamination, cannot actually be pressed against the face.
The state-of-the-art plug with protective flaps mostly concern plugs for separate optical fibers only. Recently, however, flat ribbon cables with a plurality of optical fibers have been employed, which require special plugs. In the case of these so-called MT plugs, a plurality of optical fiber end surfaces are arranged on the face in a row. A typical MT plug, for example, is disclosed in EP-A-226 274. Practical protective flaps for MT plugs which open automatically during the plugging sequence are not yet state of the art.
It is therefore a purpose of the invention to create a plug of the type mentioned in the introduction, said plug having a simple construction and wherein the protective flap reliably protects the face from contamination. The construction of the protective flap shall be particularly suited to use on MT plugs for ribbon cable. According to the present invention, this purpose is fulfilled with a plug possessing the features of claim 1.
The arrangement of the lever arm, which is formed as a flexible spring and can be detached from the plug housing, has a plurality of advantages in relation to the state-of-the-art integral form: on the one hand, the same plug housing can be employed without the protective flap, and this is desirable in many applications; on the other hand, the separate arrangement also permits manufacture of the protective flap from a material other than the plug housing, wherein optimal spring properties can be aimed at. In particular, the protective flap can be formed and fixed to the plug casing in such a way that the face is not only covered in the sense of a screen, but the protective flap can also be pressed under spring tension against the face, thus preventing contamination from dust and dirt. For this purpose, the protective flap is pressed under spring tension against the face in the closed position.
Further advantages can be achieved if the face and the inside surface of the protective flap oriented towards said face run at a angle that is offset in relation to a tangent which touches the circle described by the protective flap in the area of the end surface of the optical fiber. With that, the face and the inside surface of the protective flap oriented towards said face can be inclined at 5 to 10.degree., preferably by approximately 8.degree., in relation to a plane running at right angles to the optical axis of the optical fiber. With this arrangement, not only pressing of the inside surface of the protective flap against the face of the plug is made possible but, on springing back into the closed position, the protective flap also effects a displacement of contamination on the face in a way that can be compared to a windscreen wiper. With that, it is perfectly conceivable that the face and the inside surface assume slightly different angles in order to enhance this effect.
A particularly simple attachment of the lever arm on the plug casing is attained if said lever is snapped onto the plug casing using a snap engagement means. Accordingly, assembly is considerably facilitated and no further fixation means of any kind such as screws or similar are required.
Preferably, the lever arm and the protective flap are integrally formed from a plastic material, and likewise the plug casing, wherein said plug casing is formed from a plastic material that possesses less elasticity than the plastic material of the lever arm and the protective flap. While the spring properties are in the forefront in the case of the lever arm, the casing shall be mechanically robust and hold the optical fiber precisely. These latter properties require a relatively hard plastic material.
With an MT plug wherein, on the face, the end surfaces of a plurality of optical fibers are arranged in rows, it is particularly advantageous if the protective flap is formed in the shape of a strip and thus simultaneously covers all optical fibers.
In particular in the case of a strip-type form for the protective flap, it is advantageous if the lever arm is formed to be approximately U-shaped, wherein the ends of the U-limbs are snapped into the plug casing and can be pressed toward each another under spring tension for snapping in and removal.
With that, locking tabs or beads can be arranged on the outsides of the ends of the U-limbs which are snapped into recesses on the plug casing. With that, the lever arm with the protective flap forms a type of fork, wherein the fork prongs can be pressed together for insertion into the plug casing. Here, too, the correct choice of elasticity for the material plays a decisive role.
The recesses can be parallel hollow grooves opening towards the face, a locking piece being arranged for security on the plug casing between the U-limbs, said locking piece being gripped to the rear by the inside of the ends of the U-limbs. These openings, recessed and open to one side, can be simply manufactured using injection moulding techniques. The locking piece prevents the U-limbs from sliding out and at the same time serves to orient the positioning of the protective flap.
The opening movement, i.e. pivoting back of the protective flap under spring tension, can be realised in a particularly simple way if the protective flap possesses a run-up surface oriented away from the face, said run-up surface being inclined in such a way that, on running up a ramp on a plug counterpart, the protective flap is pivoted away. The protective flap at the same time thus possesses a control surface for control of the pivoting movement during the plugging sequence. With that, a ramp can additionally be arranged in the area of the face, the protective flap of a similar plug counterpart being pivoted away on said ramp.
Finally, it is also of particular advantage if the ramp blends into a support surface on which the protective flap of a similar plug counterpart rests after reaching the end position. The spring force taking effect on an opposing plug can, in relation to its force direction, thus be deflected in such a way that it does not reduce the force pressing the plugs together. With appropriate shaping of the support surface, it is even conceivable that this pressing force is enlarged still further.
The plug casing can be formed to approximate a cuboid and the pivotable lever arm can be held within the cuboid form within a recess. In this way, the outside dimensions of the plug are not increased by the arrangement of the lever arm. This recessed construction largely prevents unintentional pivoting of the protective flap in the unplugged state.
The individual plugs are preferably formed in such a way that, with a pair of plugs rotated in relation to each other through 180.degree. in relation to the axis of the plugs or the optical axis of the optical fiber, a plug connection can be achieved wherein, with a relative movement of the plugs towards one another, the protective flaps can be pivoted simultaneously in each case by the same components of the opposing plug.